The capabilities of UAVs have considerably developed such that UAVs are commonly used for various tasks and missions which are not necessarily military related. Nowadays, UAVs may be remotely controlled or autonomously operated on the basis of pre-programmed flight plans. However, a major drawback of a UAV is the possibility of loss of control of the UAV in the event of an acute technical failure, such as an engine failure, or such as the loss of communication with the operator of a remotely controlled UAV. In such cases, the UAV could eventually crash, thus posing a severe safety hazard, especially in the proximity of populated areas, in addition to the high cost of the resultant damage or complete loss of the UAV and its onboard systems. Therefore, authorized airspace for UAV flights is highly restricted and UAVs are generally not permitted to fly through civilian airspace. Such restrictions make it more difficult to operate a UAV and limit its potential uses.
Onboard autonomous systems may facilitate the continued controlled operation of the UAV and may assist flight and landing procedures, in the event of loss of communication with the UAV operator or in the event of an acute technical failure. Such systems are generally computer based systems which may, inter alia, determine flight routes for the UAV or select possible landing sites. Nevertheless, landing a UAV safely (safely for the surroundings and for the UAV), and moreover, landing a UAV safely in the event of an engine failure, is not a straightforward task. In addition to safety and damage prevention considerations, safe landing capability in such a scenario may contribute to fewer restrictions of UAV flights.
Reference is now made to FIG. 1, which is a top view schematic illustration of a trombone landing approach as known in the art, generally referenced 10. A trombone landing approach is a type of circling or curved landing approach or maneuver (also known as a “circle-to-land” maneuver), which is commonly employed by piloted aircrafts approaching an airport runway when straight-in landing is not feasible or desirable. There are several common patterns of circling approaches, which include several legs (flight segments) and one or more turns at different angles with respect to the runway or the preceding leg.
Trombone landing approach 10, as illustrated in FIG. 1, generally includes a downwind leg 30, a base leg 40 and an upwind leg 50. A piloted aircraft 20 is flying along trombone landing approach 10 in order to land on runway 70. Downwind leg 30 is substantially directed downwind and is substantially parallel to runway 70. Upwind leg 50 is substantially directed upwind and aligned with a centerline 60 of runway 70 to facilitate the landing of aircraft 20 on runway 70. Downwind leg 30 and upwind leg 50 are substantially straight and parallel. Base leg 40 allows aircraft 20 to perform a 180° turn from downwind leg 30 to upwind leg 50.
It should be noted that such a landing approach is commonly named “trombone” due to its geometry, which resembles the shape and manner of operation of a trombone musical instrument. The musical instrument includes a telescopic slide which allows the player to vary the length of its tube in order to produce different pitches. In the same manner, different landing approaches may be obtained by varying the length of the downwind leg of a trombone-shaped landing approach. Thus, a trombone landing approach is highly advantageous for air traffic controllers at airports when spacing between aircrafts is required, as this landing approach provides flexibility by adjustment of the downwind leg length.
Curved and circling approaches have been also used in the prior art as landing approaches for piloted aircrafts in the event of an engine failure (also known as: “glide approach”, “forced landing approach” or “180° power-off approach”). These approaches are used by pilots, commonly during flight training on light planes, in order to execute power-off landings.
U.S. Pat. No. 7,689,328, to Spinelli, entitled “Determining Suitable Areas for Off-Airport Landing”, discloses a system and a method for facilitating a safe emergency landing of a piloted aircraft or a UAV operated manually or automatically. The system includes a route analysis and planning tool which utilizes a routing algorithm to process information such as GPS data, aircraft instrumentation data and performance parameters. In a flight planning mode, the route analysis and planning tool may provide information about attainable and safe landing areas and information about the route to such a landing area. During in flight (real time) mode, the aircraft systems may provide information regarding the position, speed, heading and altitude of the aircraft, and wind speed. The route data may also be based on current data provided by the aircraft systems and may include Safe Options Limit (SOL) information and Vertical Trend Indicators (VTI). The SOL envelope provides information about the current engine out glide limits and available landing sites, accordingly. The VTI show the effect of a configuration change on the glide distance. The aircraft's systems may include an aircraft performance auto learning system. In operation, the auto learning system may utilize aircraft performance algorithms to generate performance data from flight maneuvers. The systems continue to update the performance data using current flight data.
U.S. Pat. No. 6,573,841 to Price, entitled “Glide Range Depiction for Electronic Flight Instrument Displays” discloses a method for depicting a glide range for a piloted aircraft after an engine failure. A display depicts a safe glide range. The pilot may select an airport within the glide range for emergency landing. The safe glide range is continuously computed and based on weather and wind information, airspeed, heading and computation of theoretical glide altitude, the last of which considers, at least, the aircraft's altitude and glide ratio. Additional information which may affect the glide ratio may be considered. Such information may be stored and recalled or determined by sensors.
U.S. Pat. No. 7,512,462 to Nichols et al., entitled “Automatic Contingency Generator” discloses an automatic contingency generator (ACG) for UAVs, preferably autonomous, for automatically determining a contingent route in response to contingencies experienced by the UAV, such as engine failure. The ACG continuously generates new routes to alternative destination points. In determining such routes, the ACG uses the energy state of the UAV, including relative altitude. The energy state is used to determine the UAV's glide range and to identify candidate landing locations within the glide range. Forecasted and actual wind data are used to dynamically adapt all routes for wind effects on the turn radius and climb/descent performance capabilities. The ACG may construct a route to an approach pattern or to a designated runway (including approach). Approach patterns may be stored as a part of the mission data.
U.S. Pat. No. 7,330,781 to Artini et al., entitled “Method to Determine and Guide Aircraft Approach Trajectory”, discloses a method to guide a piloted aircraft and automatically determine a transition point between a first trajectory and a second trajectory, for which a tactical landing is carried out, and so as to reach the initial point of the second trajectory under predetermined flight conditions. The trajectories are in the form of straight line segments. The predetermined flight conditions include, at least: speed, altitude, aerodynamic configuration of the aircraft, and rate of deceleration.
U.S. Pat. No. 6,438,469 to Dwyer et al., entitled “Flight Control System and Method for an Aircraft Circle-to-Land Maneuver” discloses a flight control system and method for designing and controlling a circle-to-land (CTL) maneuver of a piloted aircraft using an airborne area navigator. The pilot selects a runway which would be used for landing. The system determines an appropriate CTL maneuver according to received input, including position data, aircraft velocity data and atmospheric conditions. In addition, the system is configured to receive pre-entered or real-time data from the pilot such as the turn radius and the final approach length.
Civil Aviation Authority of New Zealand, “Forced Landing Practice”, VECTOR—Pointing to Safer Aviation, (January/February 2007): pp. 3-7, discloses basic techniques for conducting a forced landing without power in a light single-engine aircraft. These techniques include procedures which are preformed mostly manually or visually by the pilot, including confirming wind direction and speed, selecting a landing site and planning an approach. Such an approach generally includes a downwind leg, a base leg and a final approach. The base leg may be altered in order to adjust the height of the aircraft as required (i.e., turning away from the landing site if the aircraft is too high or turning towards the landing site if the aircraft is too low).